CHIANG KHONG: From February to April each year, Kam Thon spends most of her days knee-deep in the waters of the Mekong River by her village in northern Thailand, gathering river weed to sell and cook at home.

Kam Thon and other women who live by the Mekong have been collecting river weed, or khai, for decades, but their harvest has fallen since China built nearly a dozen dams upstream.

The dams have altered the flow of water and block much of the sediment that is vital for khai and rice cultivation, researchers say.

"Generally, the water is clear and the level is lower in the dry season, and we can easily wade in and harvest khai. But now, the water level is higher during dry season, which makes it more difficult," said Kam Thon, who sells khai at the local market.

"We need to spend more time collecting khai, and there is also less khai, which has affected our income," the 48-year-old said, as she rolled handfuls of the stringy green weed into balls and placed them in a nylon bag slung on her shoulder.

Kam Thon, who lives in Chiang Khong by the Thai-Laos border, said she only makes only about a third of what she used to earn when the Mekong's waters ran low in the dry season and the khai was plentiful.

Her husband's fish catch has also fallen, she said.

Stretching from the Tibetan Plateau to the South China Sea for about 4,350 km (2,700 miles), the Mekong is a farming and fishing lifeline for tens of millions of people across China, Laos, Myanmar, Thailand, Cambodia and Vietnam.

But with China building more dams to generate hydropower, fears are growing over the unseasonal flooding and droughts they cause - and for the future of Southeast Asia's longest river, which is now being shaped by powerful state-backed corporations.

Local communities and campaigners say their concerns and complaints are being ignored in the push for clean energy.

"The upstream dams are affecting fish catch, rice cultivation and river weed, a major source of income for women and the elderly," said Pianporn Deetes, campaign director for Thailand and Myanmar at Rivers International, an advocacy group.

"When the river is turned into just being a source of hydropower, it affects the lives and livelihoods of millions of people. It's about their food, their tradition and custom, their way of life," she said in an interview.

GHOST TOWNS

Eager to boost its renewable energy capacity and reduce its reliance on coal, China has built nearly a dozen dams - including five mega-dams each more than 100 metres tall - since 1995 on the Mekong, which it calls the Lancang.

China has also built at least 95 hydroelectric dams on tributaries flowing into the Mekong. Dozens more are planned in China, which is also financing others in the Lower Mekong Basin.

Energy from the hydropower dams in the Upper Mekong River Basin - comprising the Tibetan Plateau and the Lancang Basin in China and Myanmar - is valued at about $4 billion annually by the Mekong River Commission (MRC), an intergovernmental body of the Lower Basin nations of Thailand, Cambodia, Laos and Vietnam.

Yet various studies estimate that nearly all of the river's sediment load will be trapped upstream if all dams proposed in the Mekong Basin are developed, which could impact the cultivation of rice, a major food source for millions in the region.

In addition, the decline of the Mekong's fisheries - as the dams block fish migration and alter water flow - is predicted by MRC to cost nearly $23 billion by 2040, with the loss of forests, wetlands, and mangroves valued at up to $145 billion.

Communities living closest to the dams are the hardest hit, including in Chiang Khong, said Brian Eyler, who directs the energy, water and sustainability programme at the U.S.-based Stimson Center, which monitors the Mekong dams.

Releases from the reservoirs for hydropower production during the dry season can "double or even triple what natural flow would deliver," while wet season restrictions can reduce water flow by more than half, he said.

"This is causing fishing villages along the Thai/Laos border to become ghost towns," he said.

"These communities have few options for adaptation. Their elder members cannot cope with limited livelihood options, and their youth may choose to migrate or choose another livelihood, but adaptation comes with its own set of risks."

In response to such concerns, the Mekong River Commission Secretariat said the MRC - which it oversees - conducts social impact assessments, and monitors river flow and water quality for changes that could affect agriculture or communities, that are also impacted by rising temperatures and population growth.

The MRC provides "scientific and technical guidance and guidelines on dam design, construction, and operation" to manage the risks and mitigate any adverse impacts of the hydropower projects, the secretariat said in emailed comments.

But campaign groups say the MRC does not consult with local communities, and has failed to hold China accountable for the floods and droughts that have become more frequent and intense since it embarked on its dam building drive.

Chinese dams held back large amounts of water during droughts between 2019 and 2021 that saw Mekong water levels fall to record lows, exacerbating drought conditions, shows research by the Stimson Center and Eyes on Earth, a U.S-based satellite monitoring effort.

China has disputed these findings, saying there was low rainfall, and in 2020 signed an agreement with MRC to share year-round data on the flows of its portion of the river.

ENERGY DEMAND

The International Energy Agency (IEA), in a 2021 report, described hydropower as "the backbone of low-carbon electricity generation", with its potential particularly high in emerging and developing economies.

China is the world's largest hydropower market, and Chinese firms are behind over half of all new hydropower projects in sub-Saharan Africa, Southeast Asia and Latin America through 2030, according to the IEA.

Energy demand is forecast to increase by 6%-7% annually in the Lower Mekong Basin, which could see economic gains of more than $160 billion by 2040 from "full hydropower development", the MRC estimates.

But there are growing concerns worldwide over the impacts of hydropower projects, including the displacement of people.

For example, in 2018, a dam that was under construction in Laos broke and killed dozens as it swept away homes in flash flooding, denting the image of hydropower projects in the country that aims to become the "battery of Asia".

'UNPREDICTABLE RIVER'

Communities that have depended on the river for generations no longer know how to live beside it, said Niwat Roykaew, chairman of the Rak Chiang Khong Conservation Group.

"With the dams, the river has become unpredictable and their knowledge is no longer useful," said Niwat, 63, a winner of the Goldman Environment Prize in 2022.

The Mekong Dam Monitor - a collaboration between the Stimson Center and Eyes on Earth - uses satellite imagery and remote sensing to warn communities on the Thai-Laos border of changes to river flows of half a metre or more in a 24-hour period.

But this is of little use to communities that do not have other options, according to Niwat, who also runs the Mekong School in Chiang Khong that educates local children about the river, and helps researchers study the river.

"What people want - what we deserve - is co-management of the river through an inclusive, consultative process," he added.

For this current dry season through April, Kam Thon is focused on the khai harvest. On a good day, she can gather several kilos, some of which she dries in the sun in sheets that are eaten as a snack, and fetch a higher price in the market.

"It is hard to know when I can go out in the water, and how much I can harvest every day," she said.

"I need to gather as much as I can, when I can."